A mobile communication system called a W-CDMA (Wideband-Code Division Multiple Access) system or a UMTS (Universal Mobile Telecommunications System) based on Code Division Multiple Access (CDMA) has been standardized and has been in widespread use in many countries including Japan and European countries. Hereinafter, W-CDMA and UMTS will be referred to as 3G. In addition, an LTE (Long Term Evolution) system has been standardized as a next generation communication system using OFDM (Orthogonal Frequency Division Multiplexing) in which communication speed is significantly enhanced compared to the 3 G communication system.
Background Art 1
In the LTE system, it is set so that a radio base station (eNB (evolved Node B)) broadcasts system information to multiple mobile stations (UEs (user equipment) as in Non-patent Document 1, Section 5.2. According to Non-patent Document 1, system information includes an MIB (Master Information Block) and multiple SIBs (System Information Blocks). MIB includes most essential and most frequently transmitted parameters for mobile stations. SIBs include System Information Block Type 1 and other SIBs (System Information Block Type 2, etc.). SIBs other than System Information Block Type 1 are grouped into some groups and included in SI (System Information) messages. Hereinafter, System Information Block Type 1 will be referred to as SIB1, and SI messages may be represented as SI-n in which n is an integer from 1 to 32.
These system information blocks and system information messages are periodically sent from the radio base station. FIGS. 1 and 2 show examples of transmission of system information transmitted from the radio base station. As shown in FIG. 1, SIB1 is sent periodically. Non-patent Document 1 stipulates that the periodicity of SIB1 is 80 ins. However, it stipulates that the same SIB1 may be repeatedly transmitted within the 80 ms periodicity, taking into consideration of failure of reception at mobile stations. In the example of FIG. 2, the retransmission cycle of SIB-1 is 20 ms. As shown in FIG. 2, the frequency band at which SIB-1 is sent is dynamically decided by dynamic scheduling
As shown in FIG. 2, the MIB is also sent periodically. Non-patent Document 1 stipulates that the periodicity of MIB is 40 ms. However, it stipulates that the same MIB may be repeatedly transmitted within the 40 ms periodicity, taking into consideration of failure of reception at mobile stations. In the example of FIG. 2, the retransmission cycle of the MIB is 10 ins. As shown in FIG. 2, the frequency band at which the MIB is sent is fixed.
As shown in FIG. 1, SI messages are also transmitted periodically. More specifically, the SI messages are transmitted within periodically occurring time domain windows (referred to as SI-windows). For example, the cycle of SI-windows of SI-1 is 160 ms, the cycle of SI-windows of SI-2 is 320 ms, the cycle of SI-windows of SI-3 is 640 ms, and the cycle of SI-windows SI-4 is 1280 ins. Taking into consideration of failure of reception at mobile stations, in each SI-window, the same type of SI message may be repeatedly transmitted. For example, the leftmost SI-window in FIG. 2 is an SI-window for SI-1 in which SI-1 is repeatedly transmitted. The second left SI-window in FIG. 2 is an SI-window for SI-2 in which SI-2 is repeatedly transmitted. In FIG. 2, the SI-window for SI-1, the SI-window for SI-2, the SI-window for SI-3, and the SI-window for SI-4 are arranged consecutively, but since different types of SI messages have different cycles of SI-windows, it is not always true that these SI-windows are arranged consecutively in the next and subsequent rounds. In other words, FIG. 2 depicts the details of a period II in FIG. 1.
The length of the SI-window is configurable, but is 20 ms in the example of FIG. 2. When the transmission cycle of the MIB is 10 ms as described above, the MIB is sent twice in each SI-window. When the transmission cycle of SIB-1 is 20 ms, SIB-1 is sent once in each SI-window. The time periods (more specifically, subframes) and the frequency band at which SI messages are sent within each SI-window are dynamically decided by the radio base station using dynamic scheduling.
Background Art 2
In the 3G system and the LTE system, a radio base station (Node B in the 3G system, eNB in LTE system) periodically informs each mobile station whether or not call termination occurs. It is stipulated that mobile stations may use discontinuous reception (DRX) in idle mode for receiving paging messages (messages for imparting call termination) from the radio base station in (for example, Non-patent Document 2, Section 7).
Non-patent Document 2 concerning the LTE system stipulates that a Paging Occasion (PO) that is a subframe at which a paging message is sent and a Paging Frame (PF) that is a radio frame which may contain one or more Paging Occasions should be calculated by the equations below. The PO and the PF are calculated at both the radio base station (eNB) and the mobile station.
The system frame number (SFN) of a PF is given by the following equation:SFN mod T=(T div N)*(UE_ID mod N)where the value T is the DRX cycle of the mobile station for receiving paging messages, and is represented by the number of radio frames the number of radio frames. N is the least value of T and nB. The value nB is selected from among 4T, 2T, T, T/2, T/4, T/8, T/16, and T/32.
UE_ID is given by the following equation:UE_ID=IMSI mod 1024where IMSI is the IMSI (International Mobile Subscriber Identity) of the mobile station, and each mobile station knows the IMSI of the mobile station itself. The mobile station imparts its IMSI to the MME (Mobile Management Entity) that in turn imparts the IMSI to the radio base station.
In the PF thus obtained, the subframe number of the PO is given as follows.
First, index i_s is given by the following equation:i—s=floor(UE_ID/N)mod Ns where Ns the maximum of 1 and nB/T.
Next, from Table 1 or 2, the PO corresponding to Ns and index i_s is determined. Table 1 is applied for an LTE FDD (Frequency Division Duplex) system whereas Table 2 is applied for an LTE TDD (Time Division Duplex) system. In Tables 1 and 2, N/A denotes “not applied”.
TABLE 1PO whenPO whenNsi_s = 0i_s = 1PO when i_s = 2PO when i_s = 319N/AN/AN/A249N/AN/A40459
TABLE 2PO whenPO whenNsi_s = 0i_s = 1PO when i_s = 2PO when i_s = 310N/AN/AN/A205N/AN/A40156
In the periodical POs of the PFs thus obtained, paging messages are sent from the radio base station and are received at the mobile station.
Background Art 3
In the LTE system, for the PDCCH (Physical Downlink Control Channel, downlink control channel), discontinuous reception (DRX) is applied (Non-patent Document 3, Section 5.7). More specifically, when the radio base station and a mobile station are connected, and when there is no data to be communicated, the mobile station discontinuously receives a downlink control signal on the PDCCH. The period at which the mobile station receives the PDCCH downlink control signal is referred to as an on-duration. The mobile station activates its reception circuit for monitoring the PDCCH signal only in the on-durations, rather than always activating its reception circuit, so that power consumption can be reduced.
FIG. 3 shows an example of discontinuous reception on the PDCCH. In the on-durations, the reception circuit is activated, whereas the reception circuit is deactivated otherwise. The Long DRX Cycle is the cycle of the on-duration. The Long DRX Cycle Start Offset indicatives the commencement of the on-duration. The on-duration is specified by the Long DRX Cycle and the Long DRX Cycle Start Offset. The length of the on-duration is 1 to 200 subframes, and the Long DRX Cycle is 10 to 2560 subframes. The radio base station allocates the on-durations to mobile stations that are connected to the radio base station on the basis of parameters managed by the radio base station, and imparts the allocated on-duration to the corresponding mobile station.
Background Art 4
In the LTE system, when measurement of quality is conducted by a mobile station for a frequency band that is different from the frequency band in the serving cell, the serving base station allocates measurement gaps to the mobile station. In other words, if there is possibility that the serving base station handovers a mobile station to neighboring base station that uses a frequency band that is different from that used by the serving base station, the serving base station instructs the mobile station to activate measurement gaps in order that the mobile station can measure quality at the frequency band of the neighboring base station (i.e., in order that the mobile station is able to perform inter-frequency measurement).
In measurement gaps, the mobile station measures a quality at the frequency band used by the neighboring base station. In other words, the measurement gap is an inter-frequency measurement period for the mobile station to perform inter-frequency measurement. In the measurement gaps, the mobile station cannot receive signals from the serving base station. Accordingly, the serving base station does not transmit data to the mobile station in measurement gaps (Non-patent Document 1, Section 5.5.1 and Non-patent Document 4, Section 8.1.2.1).
FIG. 4 shows periodicity of measurement gaps. In the measurement gaps, the mobile station performs inter-frequency measurement, and it is communicable with the serving base station. The MGRP (Measurement Gap Repetition Period) is the repetition cycle of measurement gaps. The gap offset indicates the commencement of the measurement gap. The measurement gap is specified by the MGRP and the gap offset. The length of the measurement gaps is 6 ms (i.e., 6 subframes), and the length of the MGRP is 40 ms (i.e., 40 subframes) or 80 ms (i.e., 80 subframes) according to Non-patent Document 4, Section 8.1.2.1. The serving base station allocates the measurement gaps to mobile stations that are connected to the radio base station.